The present invention relates to vibration control systems and, more particularly, to a system and method for controlling the stiffness and damping of a liquid spring vibration control system using a single valve.
Vibration is a destructive force in a variety of environments. Vibration can be periodic, as created by a rotating compressor in an air conditioning unit or an engine in a car. Periodic vibration is characterized by a particular frequency and amplitude. Random vibration, on the other hand, has no dominant frequency and no dominant amplitude. Instead, the vibration must be analyzed quantitatively to determine average amplitudes and common frequencies. Damping is the process by which vibration steadily diminishes in amplitude. In damping, the energy of the vibrating system is dissipated as friction or heat, or transmitted as sound. The process of damping can take any of several forms, and often more than one form is present.
Liquid springs can utilize a compressible fluid to provide damping forces. A liquid spring can comprise a cylindrical housing having an internal chamber with a compressible liquid therein, a piston reciprocally disposed in the chamber, and a rod structure axially movable into and out of the chamber, secured to the piston, and having an outer longitudinal portion projecting outwardly of one of the housing ends. If a liquid spring is used between a vehicle frame and an associated wheel support structure, the compressible liquid within the liquid spring generates both stiffness and damping forces in the suspension system in response to relative axial translation between the rod structure and housing of the liquid spring caused by relative displacement between the wheel and the frame.
Although liquid springs provide stiffness or damping forces, a need exists for a way to change the amount of stiffness or damping of the liquid spring in response to changing conditions.
In an embodiment, the present invention is directed to a vibration control system for a structure having a first structural member and a second structural member. The vibration control system has a liquid spring operably interposed between the first structural member and the second structural member using a compressible liquid to generate spring forces in response to relative displacement between the first structural member and the second structural member. A second volume of compressible liquid in a second chamber is removably connected to the liquid spring by a fluid passage.
A valve is coupled to the fluid passage. The valve is selectively operable to place the second volume in communication with the liquid spring. A controller is electrically coupled to the valve. The controller emits a control signal to control the valve. The control signal is determined by a combination of at least a first component to alter the stiffness of the liquid spring and a second component to alter the damping of the liquid spring.
In an embodiment, the present invention is directed to a vibration control system where the structure is a vehicle, the first structural member is a frame, and the second structural member is a wheel. The first component of the control signal has a first pulse width, the first pulse width being sufficient to change a state of the valve for a portion of a first period. The second component of the control signal comprises a second pulse width, the second pulse width being sufficient to change a state of the valve for a portion of a second period. The controller determines the control signal by combining the first component and the second component.
In an alternative embodiment, the first component of the control signal comprises a first control signal state, the first control signal state being sufficient to change the valve from a first state to a second state for a portion of a first period. The second component of the control signal comprises a second control signal state, the second control signal state being sufficient to change the valve from a second state to a third state for a portion of a second period. The controller combines the first component and the second component to calculate the control signal.
In an embodiment, the vibration control system of the present invention has at least one of the group consisting of a height sensor, a speed sensor and a steering position sensor. The controller alters the width of the first pulse width in response to the signal from the at least one of the group consisting of the height sensor, the speed sensor, and the steering wheel position sensor. The controller alters the second pulse width in response to the height sensor signal.
The present invention, according to embodiment is directed to a method for controlling a liquid spring coupled to a second volume of compressible liquid in a second chamber by a fluid passage having a valve selectively operable to place the second volume in communication with the liquid spring. The method has the steps of receiving at least one signal from at least one sensor, and calculating at least one of a force, a displacement, a velocity, and an acceleration detected based upon the at least one signal received. The method also has the steps of selecting at least one the force, the displacement, the velocity, and the acceleration, and generating a stiffness signal based upon the selected at least one the force, the displacement, the velocity, and the acceleration. The method further contains the steps of generating a damping signal based upon the at least one signal received and combining the stiffness signal and the damping signal to obtain a control signal. The generated control signal is sent to the valve.
In an alternative embodiment, the method is for controlling a liquid spring located between a wheel of a vehicle and a frame of the vehicle. The liquid spring is coupled to a second volume of compressible liquid by a fluid passage having a valve selectively operable to place the second volume in communication with the liquid spring. The method has the steps of receiving at least one signal from at least one sensor and calculating at least one of a pitch, a roll, a warp, and a heave of the vehicle from the at least one signal received. The method generates a stiffness signal based upon the calculated at least one of the pitch, the roll, the warp, and the heave, and calculating at least one of a force, a displacement, a velocity, and an acceleration detected on the wheel. The method generates a damping signal based upon at least one of the calculated force, displacement, velocity, and acceleration detected on the wheel. The stiffness signal and the damping signal are combined to create a control signal and the control signal is sent to the valve.